The range of motion of a joint is generally measured with a goniometer. For the knee, this range of motion is typically the angle between the femur and the tibia. For many people, a desired full range of motion is between a most extended position and a fully flexed position. Typically, this most extended position will be beyond a full extension (angle of 0°) and includes hyper extension of about −5° to about −10°. The fully flexed position may be about 135°.
It is not uncommon following a knee injury or knee surgery for a patient to have difficulty moving their knee through the full range of motion, particularly extending their knee to its most extended position. Rehabilitation of the knee, by rotation of the tibia relative to the femur through a range of motion that is achievable, is typically used to attain a greater range of motion as rotation will provide benefits, such as stretching the ligaments that may limit the range of motion to a range less than desired. Rotation of a joint from any given angle toward flexion or extension and counter-rotation of the joint, where the joint has been moved generally to about a maximum angle of attainable flexion and to about a minimum angle of attainable extension, and returning to the given angle, is generally referred to as a cycle.
In an example where an anterior cruciate ligament (ACL) of the knee has been replaced, the ACL may be connected within the knee in a shorter configuration than had previously existed. This shorter connection may be advised since the new ACL may be stretched to achieve the proper length, while a new ACL that is longer than previously existed may result in a ‘loose’ knee that may never ‘tighten’ since the ACL may never shorten. Extension of the leg to stretch and lengthen a newly replaced ACL in order to properly size the ligament is generally performed by a properly trained physical therapist and typically involves pushing on the knee cap to straighten, or extend the knee coupled with other exercises.
A common technique for accomplishing such rehabilitation is to exercise a joint, such as the knee, (rotation and counter-rotation of the joint involving multiple cycles) to gradually increase the knee's range of motion, with the assistance of either a machine or by a properly trained person. Such techniques often use a hinge strapped to the knee to prevent extension or flexion into an undesired range of motion (such as, for example, less than 10° extension) while exerting a force to urge the knee toward 10° of extension. Various types of machines are known in the art for providing such rehabilitation, including those shown in U.S. Pat. Nos. 5,509,894 to Mason; 5,356,362 to Becker; 5,333,604 to Green; and 5,313,094 to Bonutti, to name a few.
However, many machines or methods may exercise a joint, such as a knee, while not providing 1.) adequate measurement of the amount of force used to urge the joint toward extension or flexion, 2.) consistent forces to urge the knee toward full flexion or full extension during subsequent cycles, 3.) adequate measurement of the angles of flexion or extension attained for the range of motion experienced, 4.) consistency in the angles of flexion or extension for the range of motion experienced during subsequent cycles, and/or 5.) a verifiable record of the therapeutic session, including angles of flexion and extension, and number of cycles.
Furthermore, many devices require constant assistance by a trained physical therapist, thereby restricting the patient's self-directed use of a device and increasing the expense of rehabilitation. What is needed, therefore, is a versatile, easy to use, and/or repeatable device for gradually increasing the range of motion of an injured or recovering knee.